Various systems have been utilized to treat spinal deformities such as scoliosis, spondylolisthesis, and others. Primary surgical methods for treatment utilize instrumentation to correct a spinal deformity and implantable hardware systems to rigidly stabilize and maintain the correction. Many of these implantable hardware systems rigidly fix the spinal column to help facilitate fusion after the column has been moved to a corrected position. In some cases, the hardware systems are intended to allow growth or other movement of the corrected spinal column.